Electromechanical delay line wherein core exhibits higher mean refractive index than envelope

ABSTRACT

A DELAY LINE COMPOSED OF A FILMENTARY CORE CAPABLE OF SUPPORTING THE PROPAGATION OF MECHANICAL ENEGERY AND A SURROUNDING ENVELOPE. THE MATERIAL OF THE CORE AND THE ENVELOPE ARE SUCH THAT THE CORE EXHIBITS A MEAN REFRACTIVE INDEX FOR THE MECHANICAL ENERGY WHICH IS HIGHER THAN THAT OF THE ENVELOPE.   D R A W I N G

United States Patent [1 1 Burner 5] July 16, 1974 ELECTROMECHANICAL DELAY LINE 3.659.915 5/1972 Maurer et ul. 350/96 wo WHEREIN CORE EXHBITS HIGHER MEAN 3,037,!74 5/]962 Bommel et al 333/30 R REFRACTIVE INDEX THAN ENVELOPE OTHER PUBLICATIONS [75] Inventor: g fgs Ulm/Donau Handbook of Chemistry and Physics, The Chemical Rubber Co., 1965, 46th Edition, pp. E-l40. 142 & [73] Assignee: Licentia Patent-Verwaltungs-GmbH, 143 relied on, QD65C4.

Frankfurt am Main, Germany [22] Filed: Apr. 28, 1972 Primary Examiner-Paul L. Gensler 1 pp NO: 248,391 Attorney, Agent, or Firm-George H. Spencer et a1.

[30] Foreign Application Priority Data [57] ABSTRACT Apr. 29, 1971 Germany ..212l2 1 3 A delay line composed of a filamentary core capable p 1971 rm l- 2 of supporting the propagation of mechanical energy and a surrounding envelope. The material of the core [52] US. Cl 333/30 R, 333/30 M and the envelope are such that the core exhibits a [51] Int. Cl. H03h 9/30 mean refractive index for the mechanical energy Field of 333/30 50/96 WG which is higher than that of the envelope.

[56] References Cited 14 Claims, 7 Drawing Figures UNITED STATES PATENTS 3,421,096 1/1969 Koester 350/96 W6 w W 5a 5a 5a! PATENTEBJUL 1 5 m4 FIG. 7

FIGS

ELECTROMECHANICAL DELAY LINE WHEREIN CORE EXHIBITS HIGHER MEAN REFRACTIVE INDEX THAN ENVELOPE The present invention relates to delay lines and it relates more particularly to so-called electro-mechanical delay lines, i.e. to delay lines in which mechanical energy derived via an input transducer from an electrical input signal, is propagated A second transducer, called the output transducer, is provided to convert the mechanical energy after passage through the delay line, into an electrical output signal.

Some conventional electro-mechanical delay lines, for example filamentary-or liquid-type delay lines, tend to suffer from either or both of the following difficulties:

a. serious high frequency attenuation (above the MHz band) and b. supports'for filamentary-type delay lines introduce signal losses and unwanted reflections.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a delay line in which at least one of the above mentioned difficulties is reduced or overcome.

According to the invention there is provided a delay line comprising a filamentary core, capable of supporting the propagation of mechanical energy, andan envelope around said core, the materials of said core and said envelope being such that said core exhibits a mean refractive index for said mechanical energy which is higher than that of said envelope.

In order that the invention may be clearly understood and readily carried into effect, the same will now be de scribed, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows, in cross-sectional view, part of a delay line in accordance with one example of the invention together with input and output transducer arrangements, and

FIGS. 2, 3, 4, 5, 6 and 7 show in cross-sectional view, part of a delay line of the kind shown in FIG. 1 and respective alternative transducer arrangements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a delay line 1 consists of a filamentary core 2 which may, for example, be a fiber of glass, around which core is provided an envelope 3. Energy is coupled into the line 1 by means. of an electro-mechanical input transducer, shown schematically by a magnetic layer 4 deposited on the cross-section of the input end of the filamentary core 1 and an electromagnet 5 carrying a coil 5a to which the electrical inputsignals are applied. The reference numerals 4', 5 and 5a indicate those components of an electromechanical output transducer which are similar to the components of the input transducer identified by the corresponding unprimed numerals.

The material of which the core 2 is constructed has a refractive index n, for the mechanical energy whereas the material of which the envelope 3 is constructed has a different refractive index, n;,, for the same energy. The corresponding speeds of sound for said mechanical energy in the core and in the envelope are C and C respectively and it is known that the two ratios C /C and ri /n areequal and the ratios will be termed the refractive power n which is a measure of the discontinuity of refractive index experienced by the mechanical energy on passing from one of said materials'tothe other. Mechanical energy can be constrained so that it is propagated (e.g. as a longitudinal wave) substantially only within the core provided.that-n n and it is desirable that the difference between the refractive indices should be as great as possible. The foregoing relationship is especially valid when the diameter d of the core 2 is large compared to the wavelength A of the mechanical energy.

If, however, d is of the same order of magnitude as A,- the delay line is only capable of propagating mechanical energy in a small number of modes. This gives rise to a predetermined distribution of energy. over the cross-section of the delay line, the distribution being such that most of the energy isconcentrated in the core 2. The delay line then exhibits a well defined phase velocity pertaining to a given mode. By selection of the dimensions of the core and the envelope, taking into account the effects of bends in the delay line, itcan be arranged that substantially the total energy in a given frequency band can be propagated in a single mode. Under these circumstances, pulsed energy propagated through the delay lines undergoes minimal dispersion and distortion so that such an arrangement is advantageous. It is important, however, that the input transducer is capable of exciting the delay line in said single mode. I

Sometransducer arrangementswill now be described with reference to FIGS. 2 to 7.

In FIG. 2 there is shown a smallportion of a'delay line 1 comprising a core 2 and an envelope 3 as described with reference to FIG. 1. At least at one end of the delay line I'there is provided a transducer arrangement comprising a magnetically responsive layer 6 deposited or otherwise provided over the cross-sectional area of the end face of the core 2,- and an electromagnet 7 which comprises a core which carries a coil to which electrical input signals can be applied or from which electrical output signals can be derived, depending-upon whether the arrangement is utilized as an input or an output transducer. The thickness t of the static forces instead of electromagnetic forces. An electrostatic layer 8 is deposited or otherwise provided over the cross-sectional area of an end face of the core 2 of delay line I. The .layer 8 and fixed electrode 8a constitute the two input or output electrodes of the arrangement. I

FIG. 4 illustrates a transducer arrangement for at least one end of a delay line 1 wherein'a magnetically prepolarized, piezomagnetic layer 9, of thickness about M2 is provided over the cross-sectional area of an end face of the core 2. The layer 9 contracts or expands longitudinally in response to electrical input signals applied to coil 7a, assuming that the end of delay line 1 shown in FIG. 4 is the input end. The layer 9 may conpractical exampleof adelay with the invention, was designedtofoperateat a fre quency of Y1 JGHZ (which corresponds to a wavelength chanical energy is utilized."

sist,- for example, of a nickel-iron alloy,- and althou'gh' of the exposed parts, isremoved, thus'providing ringthe thickness of the=layer .9 must be about M2 the thickness of theairgap is immaterialif Y The" transformer arrangement shown. in FIG. 5, uti lizes apiezoelectric'layjerl0, again of thickness about which isset into thickness oscillations'by electrical input-signals applied to oppositefaces thereof as shown. Conversely; if the. transducer; arrangement shown in FIG. Sis used'atthe output endof, the delay line -I, thelongitudinal oscillations propagated through the line lfcause mechanical comp 'essionandexpansi'on of the layer cal output signal.

' It is possible to transmit which, in turn,'provicle's an" electrienergy throiigh delay lines such as llin forms of oscillation'otherthan the longitudinal formthusfar described. In such cases the trans ducer arrangement can be such that the oscillations set shaped depressions, coline'ar 'with t'hecore, at either end of the delay line. The whole cross section of both end facesof the delay line is thenprovided with the at:-v

tive layer ofthe transducer. for example by means of an evaporation/depositionprocess ,or preferably by electroless plating These layers are thenground. or polished until only 'the activelayers deposited in the depressions formed colinearly with thelcore remain, lf desired, the active layers covering the annularend-surfaces of the envelope of the delay line need notbe com- I pletely removed. 1

' to be a discrete change.

' -What we claim is: I

upin the envelope by the transformer can be of'different form than the oscillations to be propagated through the delay line. The delay'line can, for example, be ex cited bymeans'of a transverse oscillation. Moreover, as

shown in'F IGSJ6 and 7,, transducer iarrangementscan be; usedin whichthe'activeelementdoes not actdi- E rectly upon the core 2,1but is effective thereon through f theintermediary'of the envelope 3.- In FIG. 6 a coil 11 iis iw rappedaround theenvelope 3 of delay-line l,' adja cent oneend ofjthe line and in FlG 7a piezoelectric ring, t'ransduc r 10 is provided around the envelope 3 adjacent one end lof delay-line 1. a line-in accordance of 5p.) and to -transmit the mechanical oscillations in substantially a single 'modeThe delay line 1 comprised a glass fiber of total diameter 1001,:v and'of which the dilOm, thetiber has'a storage'capacity of 1m bit and a mean access tir'neof lm sec; The complete delay line,

together with the control electrode, can. conveniently beaccommodated on a plug board. U

Although the description in the last precedinglparagraph is given by way of example only and is not intended to limitthe scope of the invention, it will be ob served that the dimensions of the'delay line are such as to'pr'esent difficulties with regard to the provision of It will be appreciated thatit-is desirable for the core at least of the delay line to consist of material of low acoustic attenuation. It is also desirable for the change in refractive index between the core and the envelope 1; Apparatus for" transmitting r'nechanicalenergy comprising in com binationz a delay line including a filamentary core, capable of supporting the propagation of 'j mechanicalenergy, and an envelope of a solid material around said core, the materials of said core and said envelope being such that said core exhibits a mean refracmeans having'anoutput co'upledto one end 'oflsaid.

tive index for said mechanicalenergy whichis higher than that of said-envelope; first mechanical-transducer delay line for causingmechanical oscillations to .be

' ameter of core 2 Thefibenwasfound to be. ca-

' pable of transmitting a bandwidth: of. 200 MHz, exhibiting a. mean attenuation of '6dB/m, With a length. of

i 3; An arrangement according to either of claim 1 in which the core consists of glass.

,4. An arrangement according to claim 3, in which the difference in refractiveindex-between the core and the envelope is discrete at least throughout the greater part of the length of-the line. e

5. An arrangement accordingto claimi, in which the;

L diameter of the core is comparable in order of magni? the various layers incorporated in the transducer ar- 5 rangement's. These difficulties can be substantially reduced in accordance with another feature of-the in'vention which provides a method of manufacturing a delay line of thekind thus far described, together with layers provided thereon for transducing purposes. In accordance with this method, the capability ,of a delay line.

having a glass fiber core to transmit light. as well as me- -The first step of the method is of the delay line,-afphoto-sensitive layer. when a photo-positive layeris used, light is injected into the envelope of the delay line and is focused thereby into the core. The light travels along the core and impinges on the inner surface of one or other of the photo-sensitive layers, so that the layers are only exposed'at their interfaces with the fibercor'e. By means of an etching protude with the wavelength'ofthe mechanicalenergy.

6. An arrangement according toclaim l, in which the core is so dimensioned that a small number of oscilla-v tion modes are capable of propagation therein.

7. An arrangement according to claim 1, in which at least one longitudinal wave is capable of being propagated in the core.

. 8 An arrangement according to'claim 1 iii which at least one of said first and second transducer means includes a magnetically active layer provided at least in o to provide, on the cross-sectional end faces at the input and output ends cess, the exposed parts of the photosensitive layers, to-

gether with a thin layer of the fiber core adjacent each the area of-the core. I v

.9. An arrangement according to claim 1, in which at leastone of said first and second transducer means ineludes, an electrostatically active layer provided at least in the areaof the core;-

'10. An arrangement-according to claim 1, wherein at least one of said first and second transducer means is a magnetically :pre-polarized piezomagnetic transformer. v 11. An arrangement according to claim 1, wherein at least one of said first or, second transducer means is a piezoelectric transformer.

12. A delay line according to claim 1, in which said first transducer means stimulates the core in a different oscillation mode from the envelope.

31, 24, 05 5 6 13. A delay line according to claim 12, in which said length of the core. I first transducer means is coupled to the core via the en- A delay line according to Claim 1, in which Said velope and stimulates an oscillation mode in the envefirst and second transducer means are coupled to the lope, the oscillation mode 1n the envelope being constituted by transverse contractions which stimulates oscil- 5 core Via envelopelations 0n the core which are propagated along the 

